1. Field of the Invention
The present invention relates to a projection lens shifting mechanism for shifting a projection lens unit in a predetermined direction, which is used in a projection display apparatus such as a liquid crystal rear projection television, and in which a light source emits a light flux to illuminate a light valve, such as a liquid crystal panel, an image is produced by the light transmitted or reflected by the light valve, the image is enlarged by a cylinder-shaped projection lens unit to be projected onto a transmission type screen. More specifically, the present invention relates to a projection lens shifting mechanism capable of adjusting the position of an image projected on a screen by translating an optical axis of a projection lens unit, and a rear projection television using the same.
2. Description of the Related Art
In recent projection display apparatuses, such as rear projection televisions, an assembly of a panel-shaped light valve including a transmission or reflection type liquid crystal panel, and a high-intensity lamp such as a metal halide lamp and an extra-high pressure mercury lamp is used instead of a CRT so as to obtain high intensity and high resolution.
The position of an image is adjusted by electrical control in CRTs. Such an adjusting technique is not easily adopted in rear projection televisions using a panel-shaped light valve. Therefore, the attaching position of an optical unit including a light valve, a projection lens unit, a lamp, and the like are adjusted so as to fit the position of an image to be projected on a screen.
However, in rear projection televisions, an optical unit including optical elements (e.g., a light valve, a projection lens unit, a lamp, and optical elements included in an illumination optical system for illuminating the light valve with high efficiency) needs to be accurately positioned and fixed in order to adjust the position of an image to be projected on a screen with high precision. To position and fix an optical unit accurately requires highly rigid and large-size parts which constitute a mechanism for shifting and positioning the optical unit. Therefore, the weight and manufacturing cost of rear projection televisions are likely to be increased.
According to one aspect of the present invention, a projection lens shifting mechanism comprises a projection lens unit in the shape of a cylinder for projecting incoming image light, a flange integrated with the projection lens unit, a projection lens mount for providing light emitted from a light valve in the shape of a plane to the projection lens unit, wherein the light valve can be optically modulated for each pixel based on image information, and the projection lens mount is concentric to an optical axis of the light emitted from the light valve, a first cam follower provided in the flange along an optical axis of the projection lens unit, a cam follower guiding portion provided in the projection lens mount for guiding the first cam follower in a direction perpendicular to the optical axis of the projection lens unit, a first lens shifting cam capable of being moved in a predetermined direction with respect to the projection lens mount and engaged with the first cam follower, for shifting the first cam follower in a direction guided by the cam follower guiding portion when the first lens shifting cam is moved in the predetermined direction, and a fixing section for integrating and fixing the first lens shifting cam and the flange to the projection lens mount.
In one embodiment of this invention, the first lens shifting cam is in the shape of a ring, and is attached to the projection lens mount in such a manner as to be capable of being rotated around light emitted from the light valve.
In one embodiment of this invention, the first lens shifting cam includes a cam hole extending in a direction tilted with respect to a circumferential direction of the first lens shifting cam, and the first cam follower is engaged with the cam hole.
In one embodiment of this invention, the first lens cam is provided between the flange and the projection lens mount, and the fixing section includes a screw and a nut to integrate the flange with the projection lens mount.
In one embodiment of this invention, the screw is provided with a compression spring so that the flange is biased toward the projection lens mount.
In one embodiment of this invention, the flange includes a second cam follower provided about xc2xc of a perimeter in a circumferential direction of the flange away from the first cam follower and along an optical axis of the projection lens unit. The second lens shifting cam engaged with the second cam follower is attached to the projection lens mount in such a manner as to be capable of being moved in a predetermined direction. The second cam follower is moved in a direction substantially perpendicular to the cam follower guiding portion when the second lens shifting cam is moved in the predetermined direction with respect to the projection lens mount.
In one embodiment of this invention, the second lens shifting cam is in the shape of a ring, and is attached to the projection lens mount in such a manner as to be capable of being rotated around light emitted from the light valve.
In one embodiment of this invention, the second lens shifting cam includes a cam hole extending in a direction tilted with respect to a circumferential direction of the second lens shifting cam, and the second cam follower is engaged with the cam hole.
In one embodiment of this invention, the second lens shifting cam and the flange are integrated and fixed to the projection lens mount by the fixing section.
In one embodiment of this invention, the light valve is of a transmission type where light is transmitted through the light valve, or of a reflection type where light is reflected by the light valve.
According to another aspect of the present invention, a projection lens shifting mechanism comprises a projection lens unit in the shape of a cylinder for projecting incoming image light, a flange integrated with the projection lens unit, a projection lens mount for providing light emitted from a light valve in the shape of a plane to the projection lens unit, wherein the light valve can be optically modulated for each pixel based on image information, and the projection lens mount is concentric to an optical axis of the light emitted from the light valve, a first cam follower provided in the projection lens mount along an optical axis of the projection lens unit, a cam follower guiding portion provided in the flange for guiding the first cam follower in a direction perpendicular to the optical axis of the projection lens unit, a first lens shifting cam capable of being moved in a predetermined direction with respect to the projection lens mount and engaged with the first cam follower, for shifting the first cam follower in a direction guided by the cam follower guiding portion when the first lens shifting cam is moved in the predetermined direction, and a fixing section for integrating and fixing the first lens shifting cam and the flange to the projection lens mount.
In one embodiment of this invention; the flange includes a second cam follower provided about xc2xc of a perimeter in a circumferential direction of the flange away from the first cam follower and along an optical axis of the projection lens unit. The second lens shifting cam engaged with the second cam follower is attached to the projection lens mount in such a manner as to be capable of being moved in a predetermined direction. The second cam follower is moved in a direction substantially perpendicular to the cam follower guiding portion when the second lens shifting cam is moved in the predetermined direction with respect to the projection lens mount.
According to another aspect of the present invention, a rear projection television comprises the projection lens shifting mechanism of the present invention.
Thus, the invention described herein makes possible the advantages of providing a projection lens shifting mechanism capable of adjusting the position of a projection lens unit included in an optical unit with high precision, i.e., capable of adjusting the position of an image to be projected on a screen with high precision.